The present invention relates to a circuit breaker, such as an autobreaker applied to a control of an electric motor, in particular, to an interlock mechanism for indicating errors that allow an operator to identify an abnormal state of main circuit contacts caused by welding thereof, on the basis of a position of a rotary-operating handle.
The basic structure of the autobreaker in which the present invention is implemented will be described with reference to FIGS. 4(a) to 4(d). In FIG. 4(a), reference numeral 1 denotes a breaker case, numeral 2 denotes a breaking section for main circuit contacts, numeral 3 is an opening and closing mechanism section, numeral 4 is an overcurrent tripping device, numeral 5 is a rotary-operating handle installed on a top surface of the case 1, numeral 6 is a gear mechanism for coupling the rotary-operating handle 5 to the opening and closing mechanism section 3 for transmission, and numeral 7 is an accessory, i.e. auxiliary switch, alarm switch, or the like.
In this case, as shown in FIGS. 4(b) and 4(c), the opening and closing mechanism section 3 comprises an upper toggle gear 3a, an opening and closing lever 3b disposed in a lower part of the breaker, a toggle link mechanism 3c for linking the toggle gear 3a and the opening and closing lever 3b, and a latch mechanism 3d, with all of these components being assembled to the opening and closing mechanism. The toggle gear 3a is coupled to the rotary-operating handle 5 via a driving gear 8 for transmission. Further, the opening and closing lever 3b is journaled so as to rotationally move in a vertical direction via a support shaft 3b-1. An urge spring, i.e. torsion coil spring 3b-2 provided on the shaft impels the lever in a direction to open the main circuit contact. The tip of the lever 3b projects to the side through a frame slot portion in the opening and closing mechanism section 3. The driving gear 8 is directly coupled to a shaft of the operating handle 5. The operating handle 5 is impelled and biased by a relatively weak return spring (spiral spring) in a direction such that it returns to the OFF position.
On the other hand, the breaking section 2 for the main circuit contacts is formed of an assembly of a fixed contact shoe 2a, a bridge-type movable contact shoe 2b, a movable contact shoe holder 2c, a contact spring (compression spring) 2d for the movable contact shoe 2b, and arc-extinguishing plates 2e. An upper end of the movable contact holder 2c is located opposite to a tip of the opening and closing lever 3b. The figure shows an ON state in which the main circuit contacts are closed. In this state, the tip of the opening and closing lever 3b is held in a position in which it retreats upward, and the movable contact shoe 2b is in contact with the fixed contact shoe 2a under the force of the contact spring 2d. 
With this construction, while the main circuit contacts are closed, the operating handle 5 is held in the ON position so as to indicate that position. Then, when the operating handle 5 is manually rotated from the ON position to the OFF position so as to open the main circuit contact, the toggle link mechanism 3c of the opening and closing mechanism section 3 releases the opening and closing lever 3b via the driving gear 8 and the toggle gear 3a. Thus, the opening and closing lever 3b rotationally moves clockwise under the accumulated force of the urge spring 3b-2 to strike the movable contact shoe holder 2c, thereby opening the movable contact shoe 2b. 
Further, in contrast, when the operating handle 5 is rotated from the OFF position to the ON position, the link mechanism 3c of the opening and closing mechanism section 3 pushes a rear end of the opening and closing lever 3b downward against the urge spring 3b-2. Thus, the opening and closing lever 3b rotationally moves counterclockwise to release the movable contact shoe holder 2c from the pressure, so that the movable contact shoe 2b moves upward under the force of the contact spring 2d, subsequently comes to contact with the fixed contact shoe 2a, and is then closed. Simultaneously, the operating handle 5 is held in the ON position to indicate that the main circuit contacts are closed.
On the other hand, if the overcurrent tripping device 4 is activated when the main circuit contacts are closed to conduct electricity through the breaker, the latch mechanism 3d of the opening and closing mechanism section 3 is released to activate the toggle link mechanism 3c. Then, as in the above-described OFF operation, the opening and closing lever 3b rotates clockwise to perform a trip operation, to thereby open the movable contact shoe 2b. In this case, the operating handle 5 is stopped at a TRIP position between the ON and OFF positions to indicate that the main circuit contacts are opened due to the trip operation. To activate the main circuit contacts after the trip operation, the operating handle 5 is rotated from the TRIP position to the OFF position to reset a latch receiver of the latch mechanism 3d, and is then rotated to the ON position to close the main circuit contact.
In the circuit breaker constructed as described above, if an excess current flows during the conduction, the contacts of the fixed contact shoe 2a and movable contact shoe 2b of the main circuit contacts may be welded together. If such contact welding occurs and is severe, the movable contact shoe 2b does not separate from the fixed contact shoe 2a, despite the fact that the overcurrent tripping device 4 of the circuit breaker is activated to cause the opening and closing mechanism section 3 to perform the trip operation. Further, the opening and closing lever 3b of the opening and closing mechanism section 3 is restrained by the movable contact shoe holder 2c and can not be rotated to the contact open position. Thus, it remains stopped at a position between the ON and TRIP positions, while pressing the movable contact shoe holder 2c. On the other hand, the operating handle 5 moves from the ON position to the TRIP position, following the operation of the opening and closing mechanism section 3 despite the contact welding. In this position, the operating handle indicates the trip operation of the circuit breaker.
Accordingly, if a maintenance worker touches the load-side circuit while performing an inspection following the trip operation based on the wrong assumption that the main circuit contacts are opened, on the basis that the operating handle 5 indicates the TRIP position, without noticing the abnormal state of contact welding, an electric shock may occur, due to the fact that the main circuit contacts of the circuit breaker are not actually open.
Thus, as measures for preventing such an accident, there is known a circuit breaker comprising interlock means that restrains the operating handle 5 to be located to a position closer to the ON position than to the TRIP position, so that the handle will not indicate the TRIP position when the contact welding occurs during the trip operation of the circuit breaker. A conventional construction of such a circuit breaker is shown in FIGS. 5(a)-5(d). That is, as shown in this figure, the opening and closing mechanism section 3 has a metallic handle lock lever 9 incorporated therein and linked therewith so as to move in the vertical direction and follow the rotational movement of the opening and closing lever 3b. An upper end of the lever 9 is located at a side opposite to a circular recess groove 5a formed in a rear surface of the rotary-operating handle 5. FIG. 5(a) is a top view showing ON and OFF positions of the rotary-operating handle 5 and a position indicating the occurrence of contact welding. FIGS. 5(b) to 5(d) show the operational states of the main circuit contact, the opening and closing mechanism section, and the handle lock lever corresponding to the ON and OFF positions and the trip operation performed when the contact welding occurs, respectively.
In this case, if the main circuit contacts are normal (contact welding does not occur), when the contacts are turned off as shown in FIG. 5(b), the lock lever 9 is lowered so as to follow the rotational movement of the opening and closing lever 3b, so that the tip thereof slips out of the recess groove 5a in the operating handle 5. On the other hand, if the overcurrent tripping device performs the trip operation to open the main circuit contact, the lock lever 9 also is lowered so as to follow the movement of the opening and closing lever 3b, as described above. Consequently, the operating handle 5 is not restrained by the lock lever 9 but can be manually returned from the TRIP to the OFF position for resetting. Further, when the operating handle 5 is placed in the ON position, the lever 9 elevates so as to follow the movement of the opening and closing lever 3b, so that the tip thereof is fitted into the recess groove 5a in the operating handle, as shown in FIG. 5(c). When, however, the operating handle 5 is rotated from the ON position to the OFF position, the lock lever 9 is lowered during the rotation so as to follow the movement of the opening and closing lever 3b, and then slips out of the recess groove 5a. Consequently, the handle operation is not hampered.
On the other hand, if the contact welding occurs during the trip operation of the circuit breaker, the opening and closing lever 3b is restrained by the movable contact shoe holder 2c and prevented from rotating to the open position, as shown in FIG. 5(d). Accordingly, the lock lever 9 is not lowered but remains fitted into the recess groove 5a in the operating handle 5. Thus, the operating handle 5 is engaged and locked by the lock lever 9 after rotating through only a small angle from the ON position, and it does not indicate the TRIP position. This allows the operator to identify the contact welding induced by the abnormal state.
There are problems with the structure and functions of the conventional mechanism shown in FIGS. 5(a)-5(d), which is installed in the circuit breaker as means for identifying the contact welding induced abnormal state, as described below.
(1) When the handle lock lever 9 is incorporated in the opening and closing mechanism section 3, it is necessary to prevent the lever from interfering with a toggle gear, a toggle link mechanism, and others that are assembled in the same opening and closing mechanism section, resulting in space restrictions. Further, the opening and closing mechanism section 3 has a complex structure, thereby requiring a time for assembly.
(2) If the contact welding occurs in the main circuit contact, even if it is not severe, a time-consuming recovery operation must be performed, in which the circuit breaker is disassembled to remove the contact-breaking section, and the fixed contact shoe 2a and the movable contact shoe 2b, which are welded together, are separated.
(3) Further, the operating handle 5, which is a resin molding, slides against the tip of the handle lock lever 9 made of metal, so that abrasion dust may be collected in the recess groove in the operating handle 5 in long usage. This dust may adhere to the movable portion of the opening and closing mechanism section 3 to hinder its smooth operation, or may adhere to a surface of the main circuit contacts to hinder electrical conduction.
The present invention has been made in view of the above points, and it is an object of the invention to provide a circuit breaker with an interlock mechanism that solves the above problems to enable the contact welding induced by the abnormal state to be identified by using a simple assembly structure and to enable the circuit breaker to be recovered from the contact welding by operating the handle and without disassembling the breaker, provided that the contact welding is not severe.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To solve the above problem, the present invention provides a circuit breaker, in which an opening and closing mechanism linked with a rotary operating handle via a gear mechanism section comprises an opening and closing lever that rotationally moves in a vertical direction so as to follow an ON operation and an OFF operation of the handle and an operation of an overcurrent tripping device. The rotational movement of the opening and closing lever opens or closes main circuit contacts disposed below the lever, and the circuit breaker indicates a state of the main circuit contacts using a position of the operating handle. The circuit breaker includes a handle lock lever for interlocking a tip of the opening and closing lever projecting to the side from the opening and closing mechanism section with a driving gear of the gear mechanism section that is located above the opening and closing lever and is directly coupled to the operating handle, so that when the main circuit contacts are opened while being welded, the operating handle is restrained to the vicinity of the ON position to restrict the movement thereof to a contact-open indicating position.
Specifically, this circuit breaker is constructed as follows:
(1) In the construction previously described, the handle lock lever is a rod that can be moved in the vertical direction by pressing a lower end thereof against the tip of the opening and closing lever and impelling the lower end from above using a spring, and the rod has a stopper section that is provided at an upper end thereof and engages, at an elevated position of the lock lever, a stage portion formed at a peripheral edge of the driving gear to restrain the operating handle to the vicinity of the ON position.
(2) In the above structure (1), the stopper section of the handle lock lever projects from the upper end of the rod toward a movement path of the driving gear, and has a stopper surface that is located opposite to the stage portion of the driving gear and is formed as an upward-inclined surface.
With the above construction, if the main circuit contacts are normal (contact welding is not occurring), the handle lock lever is prevented from interfering with the operating handle. On the other hand, when the opening operation is performed after the contact welding occurs, the handle lock lever restrains the operating handle to the vicinity of the ON position to restrict it from returning to the OFF or TRIP position. Thus, the indicating position of the operating handle allows an operator to identify the contact welding induced by the abnormal state.
In connection with the assembled structure, the handle lock lever is composed of an independent part separated from the opening and closing mechanism section, and is arranged so that the upper and lower ends of the lock lever are located opposite to the driving gear coupled to the operating handle and the tip of the opening and closing lever, respectively, to interconnect the driving gear with the opening and closing lever. This construction avoids complicated structure of the opening and closing mechanism section to allow the circuit breaker to be assembled easily. Further, the lock lever does not abut directly against the operating handle, which is a resin molding, thereby preventing abrasion dust and the resulting operational problems with the opening and closing mechanism section.
Furthermore, the upward-inclined surface is formed in the stopper section of the handle lock lever opposite to the stage portion of the driving gear. Consequently, if the contact welding occurs to cause the handle lock lever to restrain the operating handle to the vicinity of the ON position as previously described, provided that the contact welding is not severe, force can be applied to the operating handle to rotate it to the OFF position to thereby push the tip of the opening and closing lever via the lock lever using a downward vector component of force applied to the inclined surface of the stopper section. As a result, the movable contact shoe of the main circuit contact is forcibly separated from the fixed contact shoe to open the contacts.